New Trojan batteries

offgrid
offgrid Registered Users Posts: 20 ✭
in Solar Beginners Corner #1
Hello,
I have been building my system as I go, I am ready to purchase another 4 Trojans (RE 370 ah) and add them to the existing four. Should I not do this because the existing batteries were not installed at the same time. Will it be ok as it has been 42 days since the existing have been in operation ?

Thanks !
Tom
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Comments

  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #2
    Re: New Trojan batteries

    Unless your current batteries have been drawn way down regularly 45 days is not going to matter enough to worry about. 3 months, worry a bit, 6 months I would think twice, 1 year and you will shorten the life of the newest additions,

    Tony
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: New Trojan batteries

    I agree with Tony; if they've not been heavily used there should be no problem over such a short period of time.

    Check the SG of the 'old' batteries and make sure they are up to snuff. Then be sure and fully charge & equalize the whole 'new' bank to be sure you're starting off with fairly well-matched cells. Write down these initial SG readings for reference to future readings to correlate how the batteries are performing.

    And be sure you have enough charging capacity for the new total Amp/hrs.
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  • offgrid
    offgrid Registered Users Posts: 20 ✭
    #4
    Re: New Trojan batteries

    Thanks guys !
    The existing batteries are being cycled daily. As for the SG readings, I had a small issue early-on because I had to switch hydrometers and the new meter reads differently then before. However, the readings are consistant.
    As for the minimum 5% charge to the batteries, I will need at least 1 more panel to get a 36 amp needed. If my math is correct. 720ah * .05 = 36 amps
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: New Trojan batteries

    I've often told people not to get overly concerned about SG readings not matching theoretical ideals because hydrometers vary. Thanks for confirming that. :D

    Keep in mind that 5% minimum charge rate is exclusive of loads. If you're putting 36 Amps in via the charge controller but taking, say, 10 Amps out via the inverter to run loads your net charge rate is only 26 Amps. This is why we tend to shoot for 10% rate and keep loads as small as possible.

    You can have too little solar, but never too much. Sort of.:D
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